Defects may occur in the coating process as well as in any subsequent mechanical working of the surface of nickel-coated objects of light metal. The defects may consists for example in an unsatisfactory adhesion of the nickel layer to the light metal, or in polishing defects, affecting the dimensions of the coated object. Also, in service the nickel layer of the object may be damaged or chipped, rendering it unfit for use. To restore such articles to a useable state, it is necessary to remove the nickel layer, either galvanically or in a currentless procedure, so that the article may be recoated.
It is known that nickel layers may be removed with the use of a bath containing sulfuric and nitric acids. But this process requires a very long reaction time and is therefore not practical. Also special precautions are necessary in mixing the nitric acid with the sulfuric acid.